Strong Magnesium Alloys
Magnesium Alloys with Improved Castability
Magnesium alloys produced using a novel Magnesium Boride grain refiner have improved ductility and strength enabling wider use and reduced defects during manufacture.
Background Magnesium alloys are lightweight (density 1.7 g/cc vs. 7.8g/cc for steel), easily recycled and durable so providing the best solution for reducing weight in the transport sector. Efforts to reduce fuel consumption and vehicle emissions in the automotive sector have increased the demand for lightweight magnesium alloys as structural materials, particularly Magnesium Aluminium alloys. However increasing the use of these alloys to replace steel in the transport sector has been hampered by their lack of ductility and low yield strength. This is due to the large grain structure, large number of defects and large inter metallic particles formed during casting. This results in parts with poor strength and very high scrap rates during casting. Moreover it limits the design complexity of parts that can be cast with such alloys. Technology Overview Grain refiners are chemicals added at very low levels to a molten alloy in order to create a fine and homogeneous grain structure during solidification. They are commonly used in a wide range of metal alloys however no such suitable material exists for pure Magnesium, Magnesium alloys, and in particular for Magnesium Aluminium alloys. Researchers at Brunel University London have developed an effective chemically stable phase at elevated temperatures where Magnesium-rich boride, Mg1 xAlxB2, results in refinement of the grain size of the Magnesium Aluminium alloy. The grain refiner has a good lattice match that can be uniformly dispersed within the magnesium-aluminium liquid prior to solidification (casting). These stable particles reduce the nucleation barrier, promote heterogeneous nuclei and increase the nucleation density in the melt. As a result, a fine grain structure with uniform distribution of the second phase and reduced micro-porosity (<0.01%) on a fine scale, is achieved. The grain refiner can be added in powder form or as super concentrated master alloy that can be added at the foundry to the liquid metal prior to casting.
Benefits • Improves material tensile strength • Improves material ductility • Improves homogeneity in mechanical properties across the component; • Improves castability of alloys by eliminating hot-tearing • Enables the casting of large and complex shaped structures using sand moulds • Enables thin-wall cast structures; • Expected to reduce the high rejection rate during manufacture • Easily incorporated into existing process and does not require new equipment at the foundry
Enabling the use of light-weight magnesium alloys in applications where previously this has not been possible due to their low tensile strength and ductility. Enabling the casting of highly complex shaped aluminium structures where they could previously not be made due to poor castability.